In order to meet the request that semiconductor devices are made finer and caused to have higher functions, the wiring width of power supply lines arranged in the entire area of the main faces of their semiconductor chips (semiconductor elements) or the interval between signal lines arranged therein has been becoming narrower. For this reason, the impedance thereof increases or signals between signal lines of different nodes interfere with each other so as to cause hindrance to the exhibition of sufficient performances for the operation speed of the semiconductor chips, the margin of the operating voltage thereof, the resistance thereof against damage by electrostatic discharge, and others. In order to solve these problems, for example, in Patent Document 1 and Patent Document 2, package structures wherein semiconductor elements are laminated are suggested.
As a material used to stick semiconductor elements to a substrate or the like, the following examples are suggested: an example wherein a thermosetting paste resin is used (see, for example, Patent Document 3); and examples wherein en adhesive sheet composed of a thermoplastic resin and a thermosetting resin is used (see, for example, Patent Document 4 and Patent Document 5).
In conventional processes for producing a semiconductor device, an adhesive sheet or an adhesive is used to cause a semiconductor element to adhere onto a substrate, a lead frame or a semiconductor element. The adhesion is attained by attaching the semiconductor element to the substrate or the like under pressure (die attachment), and then curing the adhesive sheet or the like through a heating step.
Here, a wire bonding step is performed to electrically connect a semiconductor element that has been compression-bonded onto a substrate, etc. to the substrate, etc. After that, sealing with a sealing resin is performed by molding the semiconductor element, etc. with the sealing resin, and then curing (for example, refer to the following Patent Documents 4 and 5). When performing the above-described wire bonding, the semiconductor element on the substrate, etc. moves due to ultrasonic vibration and heat.
Therefore, conventionally, there has been a necessity to perform a heating step before the wire bonding to cure a heat curable paste resin or a heat curable adhesive sheet by heat so that the semiconductor element does not move.
About an adhesive sheet made of a thermosetting resin, or an adhesive sheet made of both of a thermosetting resin and a thermoplastic resin, a heating step is further required to keep the adhering strength certainly between the sheet and an adherend and to improve the wettability therebetween after the sheet undergoes die attachment and before the sheet undergoes wire bonding.
Patent Document 1: Japanese Patent Application Laid-Open No. 55-111151
Patent Document 2: Japanese Patent Application Laid-Open No. 2002-261233
Patent Document 3: Japanese Patent Application Laid-Open No. 2002-179769
Patent Document 4: Japanese Patent Application Laid-Open No. 2000-104040
Patent Document 5: Japanese Patent Application Laid-Open No. 2002-261233